The present invention relates to a method for mounting a ring-shaped construction on a ship stern, particularly a method for mounting precisely and easily on a ship stern in front of a propeller.
In recent years, in order to get the higher economical efficiency of a ship, the building cost has been reduced by adopting a full hull form as far as possible for the required dead weight. However, the fullness of hull form increases a turbulent flow and an inequality of flow field especially in the vicinity of the ship stern. As the result, these phenomena cause not only an increase of fluid resistance and a decrease of propulsive efficiency, but also increases of propeller cavitation, hull vibration and noise etc.
It has been found experimentally that the turbulent flow and the inequality of flow field around the propeller can be reduced by providing a ring-shaped construction which is equipped on the ship stern in front of the propeller, being not overlapped with said propeller by the detailed investigation of flow field in the vicinity of the ship stern aforementioned, resulting the reductions of necessary horse power, propeller cavitation, vibration and noise.
Said ring-shaped construction is mounted directly to the ship stern and/or through supporting members. In this case, it is important that the ring-shaped construction is mounted precisely on the ship stern.
If the accuracy of the mounting is low, the effect of said ring-shaped construction is decreased. But the ring-shaped construction is generally large in size, for instance in case of a hull of about 250,000 tons tanker, the ring-shaped construction has the following dimensions: inner diameter of about 900 cm, width of about 450 cm, and weight of about 90 tons.
It is a very difficult work to mount such a large scale ring-shaped construction precisely on the ship stern without accompanying a large amount of error.